Technical Field
Pumps for the transfer of liquids; more particularly, centrifugal pumps, and centrifugal grinding pumps.
Description of Related Art
A pump is a device used to transport liquid from a lower to a higher elevation, or from a vessel of lower pressure to a vessel of higher pressure, or to a state of low velocity to a state of high velocity. Generally, in transporting a liquid, a pump adds energy to the liquid. Typically, an electric motor or other suitable motor is used to spin an impeller or other liquid driver inside a volute casing, transferring energy to the liquid. In many instances, a pump is submerged in a pool and its discharge is connected to a pipe that is used to convey the liquid to a higher elevation. Although pumps have been known for millennia, and advances in the design and manufacturing of pumps have continued right up to the present, there remain opportunities for improvement in many aspects of pump design, such as efficiency, reliability, and manufacturing cost.
This applies to centrifugal pumps, and to grinder pumps. A grinder pump is a pump that reduces the size of solid objects suspended in the liquid. In a typical grinder pump, a cutting or grinding device is incorporated into the suction opening of the pump, which chops or reduces the size of solid objects as the pump moves the liquid. The design of the cutting/grinding device varies by manufacturer, but in essentially all centrifugal grinder pumps, the slurry from the cutting/grinding device is drawn from the cutting apparatus to the eye of an impeller. Under normal operation, the slurry passes through the impeller vanes and volute casing without problems; however problems often do occur.
Solid debris from the slurry often accumulates between the vanes of the impeller and the stationary volute casing, causing undesired friction and load on the pump motor, which reduces the efficiency of the pump. In the worst cases, the debris may block an entire vane passageway or jam the impeller. In one attempt to address this problem, long “record” (spiral) grooves are formed in the volute base surface that is proximate to the impeller vanes in an attempt to cause accumulated material to be shed from the impeller, or prevent accumulation of material on the impeller. These record grooves are of limited effectiveness, particularly with certain types of solid materials in the slurry. What is needed to address this problem is a more reliable and effective means of shedding accumulated solid material from a pump impeller and/or preventing solid material from accumulating on the impeller, which would increase the reliability and efficiency of a grinder pump.
A critical component in any liquid pump is the seal that prevents liquid from leaking from the volute along the rotating shaft into the housing that contains the pump motor. Typically a mechanical face seal is used that is comprised of two ground surfaces riding on each other with a very thin layer of liquid between them as a lubricant. Foreign material suspended in the liquid or long fibrous strands can either wrap around the seal, thereby forcing it open or eroding one or both of the ground surfaces. In either case, the seal is damaged. This is particularly the case in a grinder pump application, where the seal is exposed to a liquid slurry containing suspended solids. There remains a need for extending the life of a seal in a grinder pump, which would increase the reliability and reduce the maintenance cost of the pump while avoiding the additional cost of downtime of the pumping process.
In a related aspect, a pump may be damaged if it is run dry, even if for only a short period of time. In particular, the seal may be damaged by running the pump without having adequate liquid in the volute to maintain the seal in a wet condition. There remains a need for a pump that can be run in a dry state for a more prolonged period of time, thereby extending seal life.
The cost of energy is becoming an increasingly important consideration when selecting a pump for a given application. There remains a need for improving the efficiency of pumps, including grinder pumps, so that a given pumping output may be attained with less energy consumption by the pump.
Manufacturing cost and manufacturing precision are also important considerations in pump selection. Greater manufacturing precision results in greater pump reliability, and lower manufacturing cost results in lower purchase cost for the end user. The basic structure of a centrifugal grinder pump has remained quite complex, in that the pump includes a pump motor housing, a multi-piece pump volute, and a grinding device, which are expensive to manufacture individually, and to assemble in a reliable manner. Hence there remains a need for a pump having fewer components that are lower in cost to manufacture and assemble, and which can be assembled with greater precision, thereby resulting in greater pump reliability.